In a color diffusion transfer process, upon the imagewise exposure of a photosensitive silver halide emulsion layer, which has been associated therewith a dye image forming substance, a latent image is formed in the emulsion and is then developed by the application of an alkaline processing composition to form as the function of said development an imagewise distribution of diffusible dye or dyes or the precursors thereof. At least a portion of said distribution is thereafter diffused and transferred onto an image receiving layer, thus to form a dye image thereon.
In such color diffusion transfer processes, it is known to incorporate neutralizing layers in order to stop the excess development and/or diffusion transfer of the diffusible dye or the precursor thereof, and to stabilize the resulting dye image. It is also known to employ various types of timing layer together with such neutralizing layer in order to timely regulate the lowering of pH by the neutralizing layers.
The color diffusion transfer process is generally employed in the so-called instant photography in which processing is carried out at various temperatures. When such processing is effected at temperatures excessively lower than the room temperature, delay of the development reaction, which is considerably affected by the temperature, is brought about, and pH of the processing composition is lowered prior to the completion of predetermined development, resulting in a decrease in the maximum density or an increase in the minimum density, which obstructs the desirable dye image formation. On the contrary, in the case where processing is carried out at temperatures higher than the room temperature, because of development reaction being accelerated the lowering of pH of the processing composition is relatively delayed with the result that excess development of the silver halide emulsion takes place. In order to eliminate this defects some attempts have been heretofore made as disclosed in Japanese Patent Pre-examined Publication No. 53-72622/1978 and U.S. Pat. No. 4,061,496 by the use of a certain kind of timing layer in which permeability of an alkaline solution can be well dependent on the temperature, that is, in such a timing layer the alkaline solution is rendered more permeability at higher temperatures and less alkali permeability at lower temperatures.
However, these heretofore known timing layers have still such drawbacks that their temperature dependency is not necessarily insufficient, i.e., in the case where such timing layer can render the alkaline solution appropriate permeability at lower temperatures, relatively less permeability is given at higher temperatures, or on the contrary, when appropriate permeability is given to the alkaline solution by the timing layer at higher temperatures, the permeability thereof at lower temperatures tends to be insufficient, that the alkali permeability of such timing layers tends to change with the lapse of time or that on manufacturing polymers used for such timing layers materials harmful to the human body often have to be used. Thus few timing layers have been found to be satisfactory.
Accordingly the primary object of the present invention is to provide a photographic element for color diffusion transfer process having an excellent timing layer free of such drawbacks.